The present invention relates to a process for the production of highly effective surface treating agents. The surface treating agents produced in accordance with this invention comprise oligomeric mixtures containing pyromellitate nuclei. Many of the pyromellitate nuclei contain fluorinated ester moieties which impart water and oil repelling characteristics to various fibers.
U.S. Pat. No. 4,209,610 (Mares et al., 1980) discloses fluorinated pyromellitates useful as surface modifiers for polyamides and polyesters. One preferred group of compounds in that patent are those of the formula: ##STR1## wherein A is a fluorinated ester such as CF.sub.3 (CF.sub.2).sub.p R'O(O)C-- and wherein B is HOCH(CH.sub.2 Cl)CH.sub.2 O(O)C--; wherein R' is ethylene and p is a mixture of integers such as 3, 5, 7, 9 and 11 for different chains. Such products are formed by the reaction of pyromellitic dianhydride (PMDA) with a fluorinated alcohol, and then the reaction of the product diacid/diester with epichlorohydrin. Specifically, the product is produced by reaction of two moles of fluorinated alcohol with each mole of PMDA to form the diacid/diester. Each mole of the diacid/diester is then reacted with two moles of epichlorohydrin to produce the product. Because the oxirane may react at the one or two carbon, the product will normally contain minor amounts of material with B being HOCH.sub.2 CH(CH.sub.2 Cl)O(O)C-- (the product with a pendant primary alcohol) as well as major amounts of material with B being HOCH(CH.sub.2 Cl)CH.sub.2 O(O)C-- (the product with a pendant secondary alcohol). Other patents relating to the production of this product include U.S. Pat. No. 4,252,982 (Oxenrider 1981) wherein an ester solvent is used and U.S. Pat. No. 4,321,403 (Oxenrider et al., 1981) wherein N-methyl pyrrolidone is used as solvent. Methods for applying the compound in aqueous emulsions to fibers are disclosed in U.S. Pat. Nos. 4,192,754 (Marshall et al., 1980), 4,134,839 (Marshall, 1979), 4,190,545 (Marshall et al., 1980), 4,193,880 (1980), 4,283,292 (Marshall, 1981) and 4,317,736 (Marshall, 1982).
My copending, commonly assigned Application Ser. No. 380,188 describes a process for the production of pyromellitate oligomers useful as surface treating agents wherein a mole ratio of fluorinated alcohol to PMDA of less than 2:1 is employed.
The pyromellitate oligomers of the present invention have extremely high resistance to soiling, and soil resistant properties imparted to fibers by the oligomers of this invention are retained by the fibers after numerous laundering cycles. Therefore, fibers treated with the oligomers of the present invention will retain soil resistance properties for long periods of time in an environment where they are ultimately employed. Furthermore, as described in each of the above patents, an annealing step is employed after the application of the compound to the fiber. It would be desirable to be able to lower the temperature of the annealing step, for energy savings, without impairing either the initial soil resistance or the retention of soil resistance after laundering. With the oligomeric product mixtures of the present invention, the annealing step may be accomplished at temperatures as low as about 50.degree. C.